1. Field of the Invention
The present invention relates generally to radiation hardened circuitry, and more particularly to a communications interface and system configured to allow circumvention of a microprocessor portion thereof.
2. Description of the Prior Art
The use of components which have the highest intrinsic radiation tolerance is a logical and cost effective approach to radiation hardening. This component selection technique is routinely applied to minimize the problem of neutron degradation and total gamma degradation. It is less frequently used for radiation hardening against transient upset from prompt gamma radiation primarily because of the high degree of sensitivity most solid state components have to ionizing dose rate. Thus, hardening solid state circuits against prompt gamma radiation using component selection only works for relatively low ionizing rates less then about 1.times.10.sup.8 rad(Si)/sec. maximum, a level above which most unhardened solid state circuits can be expected to be upset. In addition, the radiation responses of individual components and circuits often aggravate other circuits to which they are connected. These synergetic effects often create upsets at levels below the individual component levels and complicate further the selection of components. Consequently, there is a need in the prior art to eliminate the necessity for selection of every component having the highest intrinsic radiation tolerance to minimize the effects of radiation. There is an additional need in the prior art to protect against prompt gamma radiation in an improved manner.
Circumvention, in its most common form, is a circuit design technique in which the outputs of critical circuits during exposure to radiation or for sometime after. A key feature of this technique is that the passage of radiation produced signals from unhardened circuits can be blocked. Circumvention techniques also embrace those designs which restore the system to preirradiation status after exposure or keep it functioning in a minimal condition until it can be restored. Cancellation techniques can also be considered aspects of the circumvention techniques.
Digital circuits and computers or microprocessors present the hardening circuits designer with a very challenging problem. Generally, computers can be expected to be upset during prompt gamma radiation and may have to be completely restarted. In some manned systems, computer restart is a valid approach, but in unmanned missiles and even in critical shipboard equipment, such as fire control systems, a better alternative is needed. Hence, there is a need in the prior art to eliminate the need to harden every circuit in a system to prompt gamma radiation by configuring the system to use certain hardened circuits along with certain unhardened circuits so as to allow the system to recovery from prompt gamma radiation.
The prior art and background, as indicated hereinabove, includes some advances in radiation hardening and recovery techniques. However, as far as can be determined, no prior art radiation recovery system for circumvention of microprocessors incorporate all of the features and advantages of the present invention.